0535 Event Schemas

Events capture the details of a specific situation or activity. They are sent between services, often using an intermediary, such as an Event Broker. Event schemas provide the means to share the structure of the information flowing in the events. They are typically attached to Topics.

EventType

An event schema begins with an EventType entity at its root. It is linked to the asset using the AssetSchemaType relationship.

The data fields in the event are represented using EventSchemaAttribute entities that are linked to the event type using the AttributeForSchema relationship.

EventSchemaAttribute

EventSchemaAttribute describes a data field or structure in an event schema. The data type of the data field is stored in an attached TypeEmbeddedAttribute classification. If the data field is a structure, the typeName property in TypeEmbeddedAttribute is set to StructSchemaType and the nested data fields, represented by their own EventSchemaAttribute entities, are linked via the NestedSchemaAttribute relationship.

Below is an example of a JSON event from the Asset Manager OMAS. It has a nested structure and this is reflected in the schema structure.

Example JSON Event

{
  "eventVersionId": 1,
  "eventType": "NEW_ELEMENT_CREATED",
  "eventTime": "date/time",
  "elementHeader": {
    "guid": "unique identifier",
    "status": "ACTIVE",
    "type": {
      "typeId": "unique identifier",
      "typeName": "name of type - eg Database",
      "superTypeNames": [
        "name of super type",
        "name of super super type etc"
      ],
      "typeVersion": 1,
      "typeDescription": "text"
    },
    "origin": {
      "sourceServer": "mds1",
      "originCategory": "LOCAL_COHORT",
      "homeMetadataCollectionId": "unique identifier",
      "homeMetadataCollectionName": "name",
      "license": "license description if any"
    },
    "versions": {
      "createdBy": "user",
      "updatedBy": "user",
      "maintainedBy": [
        "user",
        "user"
      ],
      "createTime": "date/time",
      "updateTime": "date/time",
      "version": 4
    },
    "classifications": [
      {
        "classificationName": "name",
        "classificationProperties": {
          "propertyName1": "propertyValue1",
          "propertyName2": "propertyValue2"
        }
      }
    ]
  },
  "elementProperties": {
    "propertyName1": "propertyValue1",
    "propertyName2": "propertyValue2"
  },
  "previousElementHeader": {
    "guid": "unique identifier",
    "status": "ACTIVE",
    "type": {
      "typeId": "unique identifier",
      "typeName": "name of type - eg Database",
      "superTypeNames": [
        "name of super type",
        "name of super super type etc"
      ],
      "typeVersion": 1,
      "typeDescription": "text"
    },
    "origin": {
      "sourceServer": "mds1",
      "originCategory": "LOCAL_COHORT",
      "homeMetadataCollectionId": "unique identifier",
      "homeMetadataCollectionName": "name",
      "license": "license description if any"
    },
    "versions": {
      "createdBy": "user",
      "updatedBy": "user",
      "maintainedBy": [
        "user",
        "user"
      ],
      "createTime": "date/time",
      "updateTime": "date/time",
      "version": 4
    },
    "classifications": [
      {
        "classificationName": "name",
        "classificationProperties": {
          "propertyName1": "propertyValue1",
          "propertyName2": "propertyValue2"
        }
      }
    ]
  },
  "previousElementProperties": {
    "propertyName1": "propertyValue1",
    "propertyName2": "propertyValue2"
  },
  "classificationName": "name",
  "previousClassificationProperties": {
    "propertyName1": "propertyValue1",
    "propertyName2": "propertyValue2"
  },
  "endOneElementHeader": {
    "guid": "unique identifier",
    "status": "ACTIVE",
    "type": {
      "typeId": "unique identifier",
      "typeName": "name of type - eg Database",
      "superTypeNames": [
        "name of super type",
        "name of super super type etc"
      ],
      "typeVersion": 1,
      "typeDescription": "text"
    },
    "origin": {
      "sourceServer": "mds1",
      "originCategory": "LOCAL_COHORT",
      "homeMetadataCollectionId": "unique identifier",
      "homeMetadataCollectionName": "name",
      "license": "license description if any"
    },
    "versions": {
      "createdBy": "user",
      "updatedBy": "user",
      "maintainedBy": [
        "user",
        "user"
      ],
      "createTime": "date/time",
      "updateTime": "date/time",
      "version": 4
    },
    "classifications": [
      {
        "classificationName": "name",
        "classificationProperties": {
          "propertyName1": "propertyValue1",
          "propertyName2": "propertyValue2"
        }
      }
    ]
  },
  "endOneElementProperties": {
    "propertyName1": "propertyValue1",
    "propertyName2": "propertyValue2"
  },
  "endTwoElementHeader": {
    "guid": "unique identifier",
    "status": "ACTIVE",
    "type": {
      "typeId": "unique identifier",
      "typeName": "name of type - eg Database",
      "superTypeNames": [
        "name of super type",
        "name of super super type etc"
      ],
      "typeVersion": 1,
      "typeDescription": "text"
    },
    "origin": {
      "sourceServer": "mds1",
      "originCategory": "LOCAL_COHORT",
      "homeMetadataCollectionId": "unique identifier",
      "homeMetadataCollectionName": "name",
      "license": "license description if any"
    },
    "versions": {
      "createdBy": "user",
      "updatedBy": "user",
      "maintainedBy": [
        "user",
        "user"
      ],
      "createTime": "date/time",
      "updateTime": "date/time",
      "version": 4
    },
    "classifications": [
      {
        "classificationName": "name",
        "classificationProperties": {
          "propertyName1": "propertyValue1",
          "propertyName2": "propertyValue2"
        }
      }
    ]
  },
  "endTwoElementProperties": {
    "propertyName1": "propertyValue1",
    "propertyName2": "propertyValue2"
  }
}

Asset Manager OMAS only supports one event structure so its event type is linked directly to the topic asset using the AssetSchemaType relationship. The list of data fields in the event are represented by EventAttributeSchema and linked to the event type using the AttributeForSchema relationship. Data fields such as the elementHeader have a type of StructSchemaType and its subfields are EventSchemaAttributes linked to their parent by the NestedSchemaAttribute relationship.

In the example below, EventTypeList is linked to the asset (KafkaTopic in this case) via the AssetSchemaType relationship and the event types represent each event option. The EventType entities are linked to the EventTypeList using the SchemaTypeOption relationship.

EventTypeList

EventTypeList provides an entity that holds a list of event types. It is used for an asset that produces events of different types.

EventSet

EventSet provides a specialized Collection to gather a collection of event schema definitions that are related. The event schemas are represented by the EventType entity and linked to the EventSet using the CollectionMembership relationship.

An example of an event set showing the event types used in the Open Metadata Access Services (OMAS) Out Topics.

UML Summary